From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00,FREEMAIL_FROM
	autolearn=unavailable autolearn_force=no version=3.4.4
X-Received: by 10.58.69.78 with SMTP id c14mr2689599veu.41.1400098503193;
        Wed, 14 May 2014 13:15:03 -0700 (PDT)
X-Received: by 10.50.25.4 with SMTP id y4mr187081igf.10.1400098503096; Wed, 14
 May 2014 13:15:03 -0700 (PDT)
Path: 
 eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!news.eternal-september.org!news.eternal-september.org!news.eternal-september.org!feeder.eternal-september.org!news.glorb.com!r10no4652890igi.0!news-out.google.com!gi6ni1825igc.0!nntp.google.com!r10no4652887igi.0!postnews.google.com!glegroupsg2000goo.googlegroups.com!not-for-mail
Newsgroups: comp.lang.ada
Date: Wed, 14 May 2014 13:15:02 -0700 (PDT)
In-Reply-To: <40c7405d-c4c2-4163-a430-01052b769866@googlegroups.com>
Complaints-To: groups-abuse@google.com
Injection-Info: glegroupsg2000goo.googlegroups.com;
 posting-host=66.126.103.122;
 posting-account=KSa2aQoAAACOxnC0usBJYX8NE3x3a1Xq
NNTP-Posting-Host: 66.126.103.122
References: <50562e0a-3dfa-44c4-9aaa-70cbe304b54b@googlegroups.com>
 <40c7405d-c4c2-4163-a430-01052b769866@googlegroups.com>
User-Agent: G2/1.0
MIME-Version: 1.0
Message-ID: <049c868a-e930-4e5d-a96a-611542cd1ce6@googlegroups.com>
Subject: Re: Bug or feature?
From: Adam Beneschan <adambeneschan@gmail.com>
Injection-Date: Wed, 14 May 2014 20:15:03 +0000
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable
Xref: news.eternal-september.org comp.lang.ada:19828
Date: 2014-05-14T13:15:02-07:00
List-Id: <comp.lang.ada>

On Wednesday, May 14, 2014 12:57:47 PM UTC-7, Adam Beneschan wrote:

> It does appear that GNAT may not always check the range properly when a
> function whose result is Positive tries to return a negative value due to
> overflow.  That would explain why the recursive version doesn't get an
> exception.

Here's an example:

with Ada.Integer_Text_IO;
with Ada.Text_IO;

procedure Test is
   Result : Integer;

   function Add (X1, X2 : Positive) return Positive is
   begin
      return X1 + X2;
   end Add;

   function Multiply (X1, X2 : Positive) return Positive is
   begin
      return X1 * X2;
   end Multiply;

begin
   Result :=3D Add(2_000_000_000, 2_000_000_000);
   Ada.Integer_Text_IO.Put (Item =3D> Result, Width =3D> 1);
   Result :=3D Multiply(6, 2_000_000_000);
   Ada.Integer_Text_IO.Put (Item =3D> Result, Width =3D> 1);
end Test;

Compiled without -gnato.  The result is that a negative number is output af=
ter the call to Add, but the call to Multiply raises an exception.  So it l=
ooks like when the function result is Positive, a "return" that returns the=
 result of an addition doesn't check to make sure the result is in range (w=
hen overflow is possible), but a "return" that returns the result of a mult=
iplication does check.  That would also explain why the original Buffer_Ove=
rflow test case works but the recursive Fibonacci routine doesn't.

                                 -- Adam